1. Field of the Invention
The present invention relates to a mounting apparatus of solder-balls for mounting solder-balls on a circuit substrate in a ball forming step for a BGA (Ball Grid Array) package in which IC chips are mounted on one side surface of a circuit substrate and solder-balls are formed on the other side surface, for example, among various semiconductor package forms.
2. Description of the Related Art
FIG. 1 is a cross-sectional view showing an example of a package form (BGA package) which needs a ball forming step.
In FIG. 1, reference numeral 1 denotes a circuit substrate. A bonding pattern 2 is formed on one surface (upper surface) of the circuit substrate 1, and a plurality of pad electrodes 3 which is conductive with the wiring pattern through through-hole electrodes (not shown) are formed on the other surface (lower surface).
An IC chip 4 is mounted through a bonding material such as an Ag paste or the like on the one surface of the circuit substrate 1. The IC chip 4 is connected to the bonding pattern 2 through bonding wires 5 made of metal or the like.
The IC chip 4 and the bonding wires 5 are integrally shielded with a mold resin 6. Furthermore, the other surface of the circuit substrate 1 is protected by a resist 7 except for the portions of the pad electrodes 3. Then, a solder-ball 8 is formed on each of the pad electrodes 3 formed on the other surface of the substrate 1.
The conventional solder-ball mounting apparatus used in the BGA package ball forming step and its working flow will now be described with reference to FIG. 2.
First of all, in step S1, a ball suction jig 11 and a ball feed jig 12 are brought into contact with each other as indicated by dotted arrows. The solder-balls B which are received in the ball feed jig 12 are collected on the side of the ball suction jig 11. A hollow space 13 of the ball suction jig 11 is kept under a vacuum condition by the vacuum suction. As a result, the solder-balls B are sucked by respective ball suction holes 14 in communication with the hollow space 13.
Subsequently, the ball suction jig 11 and the ball feed jig 12 are turned over together upside down, and thereafter, are separated away from each other as indicated by dotted arrows. At this time, the solder-balls B are held under section on the respective ball suction holes 14 of the ball suction jig 11 by the suction force caused by the vacuum suction. The solder-balls B other than the sucked balls fall down toward the bottom of the ball feed jig 12 by their gravitational force.
It should be noted that there is another method for sucking the solder-balls B to the ball suction holes 14 of the ball suction jig 11, in which the solder-balls B are aligned on a ball alignment jig 15 in advance in accordance with the arrangement of the ball suction holes 14, and the balls are sucked to the ball suction holes 14 of the ball suction jig 11.
On the other hand in step S2, a suitable amount of flux F is applied to a plurality of pad electrodes (not shown) formed on the circuit substrate P by using a coating nozzle 16.
Subsequently, after the ball suction jig 11 has been positioned above the circuit substrate P, the ball suction jig 11 is moved toward the circuit substrate P. The solder-ball B suction-held by the ball suction holes 14 are fed on the bad electrodes (not shown) of the circuit substrate P through the flux F. Furthermore, the vacuum suction of the ball suction jig 11 is stopped so that the hollow space 13 is returned back to the atmospheric pressure. As a result, the solder-balls B are released from the ball suction holes 14 and are mounted on the circuit substrate P by the adhesion of the flux F.
Thereafter, the circuit substrate on which the solder-balls B have been thus mounted are fed and heated in, for example, a reflow furnace so that the solder-balls B on the circuit substrate P are molten to form spherical solder-balls B on the pad electrodes. Thereafter, the flux component which resides on the surface of the circuit substrate P is removed through a cleaning step.
However, the above-described conventional amounting apparatus suffers from the following disadvantages since very fine and light-weight solder balls having a diameter of 1 mm or less are handled.
(1) A coating film such as a thin oxide film or a contamination film is formed on surfaces of the solder-balls received in the ball feed jig 12 so that static electricity is charged on the ball surfaces and the solder-balls are liable to be adhered to each other. For this reason, when the solder-balls B are sucked by the ball suction holes 14 of the ball suction jig 11, the other solder-balls B are adhered to one hole like grapes. Accordingly, in order to suck the solder-balls to respective ball suction holes 14 one by one, such a troublesome work that the extra solder-balls B are removed after the suction of the solder-balls B or the solder-balls B are aligned on the ball aligning jig 15 as described above is necessary.
(2) In order to positively suck the solder-balls B on all of a number (100 to 400) of ball suction holes provided in the ball suction jig 11, it is necessary to turn over the ball suction jig 11 as described above. This is troublesome and becomes a hindrance against the automation.
(3) When the solder-balls B are fed to the circuit substrate P by the ball suction jig 11, the adhesive force of the flux F is weak, and the solder-balls B would be left on the ball suction hole 14 only by returning the hollow space 13 back to the atmospheric pressure. For this reason, the appearance inspection is carried out after mounting the solder-balls B on the circuit substrate P. In the case where a ball mount removal (i.e., the pad electrodes on which the solder-balls B have not been mounted) is found, a repair work is necessary.